1. Field of the Invention
The present invention relates to a cant angle sensor assembly for use in sensing the tilt of an object such as a body of an agricultural tractor to generate an alarm signal or a signal for controlling a position of the agricultural tractor relative to a working machine, and particularly, to such a cant angle sensor assembly comprising a pendulum serving as a sensing member and pivoted on a supporting system adapted to be mounted on an object whose cant angle is to be detected, for swinging movement in a direction of tilt of an object; a movable electrode plate formed on the pendulum; two stationary electrode plates fixedly mounted on the supporting system in an opposed relation at a given gap to the movable electrode plate, so that with the swinging movement of the pendulum, the areas of the two stationary electrode plates opposed to the movable electrode plate are increased and decreased in a manner contrary to each other; and an electric circuit arranged to detect an electrostatic capacitance between the movable electrode plate and each of the two stationary electrode plates to provide a voltage corresponding to the tilt or cant of the object.
2. Description of the Prior Art
In such prior art cant angle sensor assembly, as disclosed, for example, in Japanese Patent Publication No. 53485/84, the movable electrode plate has been formed on one flat surface of the pendulum and therefore, it has been difficult to form the movable electrode plate to have a wider region on a flat surface of a pendulum of a limited size, resulting in a failure to provide a wider sensing range of cant angles of the object.
In addition, in the above prior art assembly, if the pendulum vibrates due to an external disturbance such as vibration, an input received by the electric circuit becomes unstable, failing to exactly sense the tilt of the supporting system. Therefore, in order to damp the vibration of the pendulum, an oil damper has been provided which utilizes a viscosity resistance of oil to impart a damping force to the pendulum. However, in the prior art assembly including such an oil damper, not only is there a problem in performance in that due to the viscosity of a braking oil varying depending upon the level of temperature, the damping characteristics of the oil damper largely varies at lower and higher temperatures, resulting in an unstable accuracy in sensing the cant angle, but also there is an economical problem that the construction is complicated and costly from the necessity for oil seal means for preventing leakage of the braking oil.
Further, in the cant angle sensor assembly, to exactly sense the tilt of the supporting system, a slight variation in electrostatic capacitance between the common electrode and each of the two stationary electrodes attendant on the displacement of the sensing member must be detected with accuracy, but the electrostatic capacitance is liable to be influenced by a floating capacitance and extraneous noise. Thereupon, to prevent a reduction in sensing accuracy due to such influence, the above prior art assembly is constructed such that the electrostatic capacitance detecting portion is enclosed by a magnetic shield, and this causes an unavoidable complication of structure.